/Engine/Source/Runtime/Engine/Classes/Engine/World.h
Sometimes there is a need to duplicate additional element after duplicatingUWorld. If you do this using this event you need also fill ReplacementMap and ObjectsToFixReferences in order to properly fix duplicated objects references.
typedef [TMap](API\Runtime\Core\Containers\TMap)< [UObject](API\Runtime\CoreUObject\UObject\UObject) *, [UObject](API\Runtime\CoreUObject\UObject\UObject) * > FReplacementMap